This invention relates to an engine and a power transmitting system for a small boat, such as a water jet propulsion craft, and more particularly to an improved arrangement for connecting an engine output shaft to a propulsion unit input shaft and an arrangement for balancing the engine within the craft against undesirable operational forces tending to render the craft unstable.
The use of water jets for propulsion units in a wide variety of watercraft is well known. One of the more popular types of such watercraft is a small, single rider unit that is designed to be operated by a rider sitting in a straddle fashion and wearing a swimming suit. With this type of unit, the engine should be mounted at a generally forward location so as to improve the balance of the unit and provide sufficient room for the rider. However, it is also desirable for the water jet to be placed at the rear of the watercraft, and this means that its impeller is spaced a substantial distance from the driving engine. As a result, the drive shaft is very long and it is normally the practice to support the drive shaft by axially spaced bearings. There are often difficulties, however, in radially aligning the bearings, drive shaft, engine output shaft and impeller assembly. Unless properly aligned, the drive unit can cause undesirable vibrations which may be transmitted to the hull of the watercraft and cause discomfort to an operator.
When connecting an engine output shaft to an impeller shaft, it has been known to interpose a vibration dampening rubber coupling in order to prevent any rotational vibration of the output shaft from being transmitted from the engine to the impeller shaft. Also, it has been known, to divide the impeller shaft of the propulsion unit into two halves, a forward half and a rearward half, to be connected together through a key or spline coupling. Such a coupling is often journaled for rotation within a vertically extending bulkhead wall separating the engine compartment from the impeller assembly compartment. The coupling is journaled within a bearing assembly at the bulkhead wall. The bearing assembly is often provided with an elastomeric vibration dampening member between itself and the bulkhead wall in order to prevent engine vibrations from being transmitted to the hull.
While it is often desirable to utilize a soft rubber coupling between the engine output shaft and the impeller shaft, or a soft elastomeric mounting arrangement between the bulkhead wall and the bearing assembly rotatably journaling the power transmitting shaft arrangement, in order to maximize vibration dampening; the softness of the dampening members which may in fact be employed has been limited in order to secure a sufficient durability for such members. Thus, it has been unavoidable that some rotational vibration and engine vibration are transmitted to the craft's hull.
It is, therefore, a principal object of this invention to provide an improved arrangement for connecting an engine output shaft to a watercraft propulsion unit.
It is further an object of this invention to provide for improved vibration isolation capability in an elastomerically dampened coupling and support arrangement for the power transmitting shaft system of a small watercraft which also possesses a high degree of durability.
It is yet a further object of this invention to provide a durable, vibration dampened coupling and support arrangement for the power transmitting shaft system of a small watercraft which is capable of efficiently transmitting power from the craft's engine to the propulsion unit.
It has been known that reciprocating internal combustion engines give rise to numerous unbalanced forces that can cause vibration. The reciprocation of a piston within a cylinder generates one inertial force in accordance with the reciprocating movement of the piston. This inertial force is exerted upon the crankshaft and can cause vibrations unless balanced. In addition to these forces, it is a common practice in multiple cylinder engines to offset one cylinder and connecting rod from that of an adjacent bank. This is frequently done so that the connecting rods can cooperate with a single throw of the crank. When offset connecting rods are employed, a force couple is exerted on the crankshaft in addition to the force mentioned above. Of course, such force couples also can give rise to vibrations and shakes if not appropriately balanced.
It is well known to employ counterweights on the crankshaft throws so as to balance the inertial forces generated by the reciprocation of the pistons. In many instances, it is difficult or impossible to provide sufficient counterweighting directly on the crankshaft so as to dampen all such forces. This problem is particularly acute when the engine is extremely compact, which is always desirable. Additionally devices must be employed to balance the force couples. All of this balancing arrangement can often be extremely complicated and cumbersome.
A related problem involves the rotational momentum achieved by a crankshaft assembly of an engine when such forces are not adequately counterbalanced. Such rotational momentum can be imparted to an associated vehicle, such as a jet propelled watercraft, thereby tending to destabilize the craft during its operation upon a body of water.
It is, therefore, still a further object of this invention to provide an improved and simplified balancing arrangement for an internal combustion engine.
It is yet a further object of this invention to provide a simple and compact balancing arrangement which will counter rotational forces of a crankshaft assembly which would otherwise tend to destabilize a watercraft during operation.